Reid and Specter know what it's like to poll under 50 percent for an entire cycle but come out victorious. Reid won his 1998 race by just 428 votes. Specter squeaked out a 49 percent win in 1992.

Given current polling numbers, Reid would need a third-party contender to take at least 17 percent of the vote.

Today, however, all three are in a tougher spot than they've ever faced before.

At the end of October 1998, Mason-Dixon polling in Nevada had Reid narrowly ahead of then-Rep. John Ensign (R), 47 percent to 45 percent, and his favorable/unfavorable ratings were pretty decent at 49 percent to 36 percent. Compare that with the latest Mason-Dixon poll out this weekend, in which Reid is losing to every potential GOP challenger and has a favorable to unfavorable rating of 33 percent to 51 percent.

ADVERTISEMENT

In Pennsylvania, a poll taken in April 1992 showed Specter under 50 percent but still ahead of his Democratic opponent Lynn Yeakel, 47 percent to 34 percent. His favorable/unfavorable ratings were 49 to 42 percent. Specter is down 10 points to Pat Toomey (R) among likely voters in the most recent Franklin & Marshall poll, with favorable/unfavorable ratings at 32 percent to 45 percent. A new Quinnipiac poll out today does show Specter leading Toomey for the first time since May, with a favorable rating 12 points higher than in the Franklin & Marshall poll. But it's important to note that Specter's opponents haven't spent a dime yet.

In Arkansas, Lincoln had never won less than 53 percent of a congressional vote and she'd enjoyed consistently solid marks among voters. In the days before her first Senate win in 1998, a Mason-Dixon poll showed her favorable rating at 57 percent. Polling taken by the University of Arkansas in October of 2003 showed her job approval at 55 percent. Fast-forward to this January and you wonder if voters were thinking about the same person: A Mason-Dixon poll showed Lincoln's favorable ratings at just 39 percent, with 41 percent disapproval.

Is there a light somewhere at the end of the tunnel for these Democrats? Or is this the end of the line?

In recent history, there have been a couple of examples of a candidate polling this badly and going on to win. One way, of course, is to have a credible third-party candidate siphon off enough anti-incumbent votes to let the sitting senator squeak in. The most recent and best-known example was Sen. Charles Robb's victory in 1994. The Virginia Democrat's numbers in the fall of 1994 looked as bad as Reid's do today. His favorable/unfavorable ratings in October were 29 percent to 44 percent, and he was stuck at 33 percent (and second place) from September until November, when he pulled into the lead with 37 percent. Robb beat Republican Oliver North by 46 percent to 43 percent, with former state Attorney General Marshall Coleman (I) taking 11 percent.

Polling taken in Nevada recently has shown the possibility of a "Tea Party" candidate taking anywhere from 9 percent to 22 percent. But given that polls show Reid getting only 39-42 percent of the vote in a two-way contest, he'd need a third-party contender to take at least 17 percent of the vote. That's going to be tough, even for a well-known and well-funded candidate.

Another comeback scenario unfolded in the 1992 New York Senate race, when Sen. Alfonse D'Amato (R), who was running behind his Democratic opponents for most of the year, squeaked out a 49 percent to 48 percent win over state Attorney General Robert Abrams (D). Polling taken for the Buffalo News that April showed D'Amato trapped somewhere between 34 and 40 percent and losing to two of the three potential Democratic candidates. But a contentious Democratic primary, which left the party still struggling to unify in the fall, allowed D'Amato to drive the debate for the last few weeks of the campaign and change the momentum of the race.

But this year, while Republicans do have crowded primaries in Arkansas and Nevada, both will be over before summer even kicks in (May 18 and June 8, respectively). Of course, Specter and Lincoln have primaries of their own to worry about, which means they have less time, money and energy to spend on their opponents.

There's great overlap between sports and politics. In both, money, talent and statistical advantages matter. But in the end, a come-from-behind victory is much more attainable in sports than in politics.